Method and apparatus for making electron tubes



Aug. 15, 1961 J. A. MCCULLOUGH ETAL 2,996,347

METHOD AND APPARATUS FOR MAKING ELECTRON TUBES Filed Dec. 5, 1957 3 Sheets-Sheet 1 &5 1

A INVENTOR;

Jack ,4. MC'u//oqyfi ATTORNEY Aug. 15, 1961 J. A. M CULLOUGH ETAL 2,996,347

METHOD AND APPARATUS FOR MAKING ELECTRON TUBES Filed Dec. 5, 1957 3 Sheets-Sheet 2 ATTORNEY Aug. 15, 1961 J. A. M CULLOUGH ETAL 6, METHOD AND APPARATUS F OR MAKING ELECTRON TUBES Filed Dec. 5, 1957 3 Sheets-Sheet 3 ATTORNEY United States atent 2,996,347 METHOD AND APPARATUS FOR MAlHNG ELECTRON TUBES Jack A. McCullough, Los Altos, and William R. Stuart,

Millbrae, Calif., assignors to Eitel-McCullough, Inc.,

San Bruno, Calif., a corporation of California Filed Dec. 5, 1957, Ser. No. 700,853 Claims. (Cl. 316-19) This invention relates to a method for making electron tubes and to apparatus for performing the method. More specifically, the invention relates to a method and apparatus for making electron tubes having prmsure seals. The term pressure seal is defined for use herein as a permanent, vacuum-tight seal obtained by the application of pressure at temperatures below the melting point of any of the materials in the seal.

The construction of electron tubes is such that practically all types have a shell or envelope involving at lease two sections sealed together along an annular joint. In the past it has been standard practice to join envelope sections by means of fused or melted bonds, such as the conventional braze or Weld joint. It has previously been proposed that a vacuum-tight seal could be made at temperatures below the melting point if the surfaces to be joined were given an optical polish. This optical polish technique has never been adopted commercially for a number of reasons including the fact that optical polishing is expensive.

The present invention has as a basic object the teaching of a method and apparatus by which electron tubes can be made with pressure seals on a commercially practical basis.

A more specific object of the invention is to provide a pressure sealing method and apparatus having a very short processing cycle. An associated object of the invention is to provide a pressure sealing method and apparatus in which heating of the seal is accomplished by inducing an RF current directly in the metal surfaces to be sealed together.

A further object of this invention is to provide a pressure sealing method and apparatus which does not involve the expense of obtaining an optical polish on the surfaces to be joined.

An additional object of the invention is to provide a pressure sealing method and apparatus which eliminates need for the usual exhaust tubulation on tubes. An associated object is to provide a pressure sealing method and apparatus which combines into a closely related system and apparatus for formation of the pressure seal and bakeou-t, and cathode formation.

Another object of the invention is to provide an electron tube having an envelope comprising two members joined together by a pressure seal.

In essence, the invention resides in the making of electron tube pressure seals by the application of high pressures and high temperatures in a vacuum. Although high temperatures are utilized they are of course below themelting point of any of the materials involved in making the seal.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the invention. It is to be understood that the invention is not limited to the disclosed species, as variant embodiments thereof are contemplated and may be adopted within the scope of the claims.

FIGURE 1 is a side view partly in section showing a vacuum chamber and pressure exerting ram in accordance with the invention. An electron tube is shown in the the normal tube processing procedures such as exhaust,

,, 50 supports a conventional hydraulic cylinder chamberand the ram is positioned in pressure exerting contact therewith;

FIGURE 2 is a cross-sectional view showing the vacuum chamber of FIG. 1 on an enlarged scale. The tube is shown in cross section, and the position of the ram is such that it is not exerting pressure on the tube;

FIGURE 3 is a view on the line 33 of FIGURE 1;

FIGURE 4 is an enlarged top view of the tube holding jig of FIGURES 1 and 2; and

FIGURE 5 is a side view of a completed tube of the type shown in FIGURE 2.

Referring to the drawings in more detail, FIGURE 5 shows an example of a tube 10 made by the method and apparatus of the invention. The particular tube shown in the drawings is cylindrical in shape and has an envelope wall made of a plurality of ceramic rings 11 and a plurality of metal rings 13-22. FIGURE 2 shows the tube 10 in cross-section, and the construction of the tube can be best understood by viewing both FIGURES 2 and 5. It will be noted that the tube is a double triode so that metal rings 14 and 21 both form anodes at the ends of the tube. Metal rings 15 and 20 form supports for control grids; rings 16 and 19 form cathode supports; and rings 17 and 18 form leads for the single heater which is inside the double cathode. The end rings 13 and 22 are merely to protect the anode rings against damage. Each of the electrode rings is provided with a terminal tab for which primed reference numerals are employed. The terminal tabs are arranged in two diametrically positioned rows.

Although a specific tube has been disclosed for convenience in describing the method and apparatus, it will be understood that other tube configurations can be made by the invention.

Coming now to the apparatus of the invention, FIG- URE 1 discloses the stand pipe 30 of a conventional exhaust pumping system (not shown). At the upper end of pipe 30 a Water cooled mounting disk 33 is attached as by brazing, and a sealing ring 35 is seated in a recess on the upper surface of the disk. A support ring 37 is attached vto disk 33 by means of screws 38. A base member or plate 40 is mounted in' the center of support ring 37 by means of screws 41. As shown best in FIGURE 2, the base plate 40 has a central aperture 43 and two side apertures 44. In addition, the plate 40 has a central seating recess 45 and an annular recess in which sealing ring 47 is positioned. A coil of tubing 48 encircles plate 40 in the area of seal 47 to permit cooling of the seal.

A platform 50 is mounted on support ring 37 by means of three rods 51 which are attached to ring 37 by screws 52 and the platform 50 by screws 53. In turn, platform and piston unit 55 by means of three rods 56 held in place by screws 57. The cylinder and piston is connected by pipes 60 and 61 to a conventional hydraulic pumping system (not shown).

A piston rod 63 extends down from the unit 53 and 65. A rod 67 is accurately guided by a bushing 69 which is mounted on platform 50 by screws 70. Rod 67 fits into coupling 64 with considerable play in order to accommodate any misalignment between bushing 69 and the piston rod 63. A coupling 72 is mounted on the end of rod 67 where it is held in place by a screw 73 which engages a recessed wall portion 75 on rod 67. The rod 67 has an accurately machined close fit in coupling 72, and the recess 75 is provided so that the screw 73 will not roughen the accurately machined portion of the rod.

The lower end of coupling 72 has a recessed portion lined with two sealing rings 77 and 78. A cooling tube 79 is attached to coupling 72 to prevent heating of'the -sealing. rings. A- glass, cylinder 80 is held in the end of -coupling 72 by frictional engagement withsealing rings 77 and 78. A ram 82 is held wedged between the recessed end of coupling 72 and the upper end of cylinder r 80. Ram 82 is made of ceramic or other dielectric material having high strength and low heat conductivity.

1%. tubular coil 85 surrounds cylinder 80 about at the .centeri thereof. Radio frequency current 'is passed along :thecoil 85 and cooling water is passed therethrough. The coil is arranged to move up and down with the cylin- .:der, as will now be described. A platform 87 of insulat- ;ing material is split at one end and clamped to coupling 72 by means of screw 88. The ends of the coil 85 are cattached to platform 87 to support the coil and are provided with fittings 89 for connection to flexible water Zhoses. The ends of 'coil' 85 and the fitting are joined .to? metal plates 90 which are attached to platform 87 and :towhich flexible copper strap leads 91 are attached by -screws92. The leads 91 are connected to a conventional source of radio frequency power (not shown).

. The structure thus far described provides the operating mechanism for making a tube according to the invention. The remaining structure shown within the cylincder 80 in FIGURES 1 and 2 consists of the tube and 'the jigging for it. The tube has already been de- :scribed. It will be seen best in FIGURES 2 and 4 that 'the tube parts are loaded in a cylindrical jig 94 having a central bore 95 and longitudinal grooves 96. -'Ihe grooves 96 must be at least equal in number to the numberof rows of terminal tabs on the tube, assuming of course that the tube under construction has this type of .terminal arrangement. It will be seen in FIGURE 4 ithat jig 94 has four grooves 96 whereas tube 10 has only two rows of terminal tabs. The two extra grooves are desirable for free passageof air from the tube to the exhaust chamber. Jig 94 is made of dielectric material :such as ceramic.

The jig 94 is supported on a. cylindrical stand 98 which is received in the seating recess 45 in plate 40. A short elevating ring 100 is received in the upper end of stand 98. A pressure ring 102 rests on the top of the tube and -is provided with a central bore 103. Ram 82 is provided .with a tapered tip 104 which engages the rim of bore 103 to assure even application of pressure. Stand 98 and the rings 100 and 102 are made of ceramic or other dielec- -tric material having high strength and low heat conductivity.

Jig 94 is provided with two apertures 106 opening into diametrically opposed recesses 96 so that electrical con nection can be made to heater tabs 17 and 18'. The connection'is made by leads 108 and 109 which pass .throughaperture 44 in plate 40 and are connected to terminals 110 and 111 which are mounted on but insulated from stand pipe 30. The upper ends of leads 108 and 109' FIGURES 1 and 2 show a tube 10 positioned inside the :vacuum-tight chamber formed by the base member 40 in cooperation with the wall structure comprising cylin- .der 80 and coupling 72. Naturally, the first stepsis to .insert the tube parts into the vacuum chamber. Pref- ;erably the tube parts, such as parts 13-22, are loaded intothe jig, such as jig 94.11am placing the jig in the -vacuum chamber. In practice it is desirable to assemble stand 98, ring 100, jig 94, the tube parts, and ring 102 outside the vacuum chamber and insert them as a unit. It will be apparent from FIGURE 1 that by operating the cylinder and piston unit 55 to raise piston rod63, the glass cylinder 80 can thereby be lifted so that its bottom edge is above theposition oi ring 102 to permit easy insertion of the tube and associated ceramic parts 98,

100, 94 and 102. w a

1 1 (Atterjthe tube and associated" ceramic parts have been 4 placed in processing position with stand 98 seated in recess 45, the ends of heater leads 108 and 109 are inserted through slots 106 so that the contact fingers on the leads engage the heater terminals 118' and 117'. Next, the cylinder and piston unit 55 is operated to lower the glass cylinder until its lower endmakes sealing contact with sealing ring 47 but before ram 82 makes contact with ring 102, as shown in FIGURE 2.

Next the stand pipe30 is connected, as by suitable valving,.to a conventional vacuum system to obtain a vacuum in the cylinder 80 and hence within tube 10. At this point it should be explained that the separate metal and ceramic envelope parts have sealing surfaces which are not provided with an optical finish. In fact,'the sealing surfaces which are pressed together need not be polished at all, although coining to obtain flatness is desired.

In addition to saving the expense of optical polishing, the use of sealing surfaces which have a finish rougher than an optical finish permits the tube to bequickly and fully pumped in a vacuum chamber without resorting to some means for holding the sealing surfaces separated during pumping. It will be understood by those skilled in the art that if the sealing surfaces have an optical polish they will fit so closely together that the passage of gas therebetween will be at best so slow as to require an unreasonably long pumping period.

.After connecting the vacuum chamber to the pumping system, the tube is heated and allowed to outgas for a period commensurate with its size. .At this point it is desired to emphasize the fact that the heating is accomplished by inducing a radio frequency current directly into the metal portions of the tube. In addition to any beneficial elfect the high frequency current may have in the action which causes the sealing surfaces to bond together upon the application of pressure, the direct induction of radio frequency current eliminates the prolonged heating and cooling period which would be required if a conventional oven type of heating were employed. In this connection it should be understood that one of the reasons for making parts 98, 100, 102, 82, and particularly jig 94 out of dielectric material is so that they will not prevent or diminish the induction of current in the metal parts of the tube.

Similarly, it will be appreciated that the elimination of metal as the material for parts which are subject to high temperature makes it possible to raise cylinder 80 immediately after forming the pressure seals. If metal were used it would be necessary to have a cooling period within the vacuum, as otherwise oxides would form and destroy 'the tolerances for parts 98, 100, 102, 104 and particularly 94.

During the outgassing period any required cathode forming is accomplished. The particular tube shown in the drawings employs a conventional oxide coated cathode. Forming of the cathode is accomplished by applying power to the leads 108 and 109 which energizes the heater to the extent necessary to raise the cathode to forming temperature.

When forming of the cathode and outgassing has been completed, thenext step is to make the pressure seals.

The pressure seals are made by operating the cylinder and piston unit 55 to move piston rod 63 downwardly until ram- 82 engages pressure ring 102 with suflicient force to apply to the sealing surfaces a unit pressure substantially in excess of that which would be provided by exposing the outside of the tube to atmospheric pressure with a vacuum on the inside. It should be understood that evacuation of the vacuum chamber and induction heating of the sealing surfaces are continued when the sealing pressure isapplied. After the sealing pressure has been applied and a vacuum tight seal has been formed, the heating current in coil is cut ofli, stand .pipe 30 is disconnected from from the vacuum pump, cylinder 80-is raised, tube 10 and jig 94 are removed from ing and the application of pressure. The point is that surfaces to be pressure sealed must be almost entirely free of dirt, occluded gases, oxides and other impurities. One of the best ways of accomplishing such cleaning is ,to heat the surface in a non-oxidizing environment, as

for example in a vacuum or inert gas. Incidental to this understanding is the realization that the method of the invention can be used to make gas filled tubes employing one of the inert gases such as helium, or other gases such as hydrogen where the other gas does not form compounds with any of the particular metals out of which the sealing surfaces are made. Naturally, it is not only necessary that the sealing surfaces be cleaned sometime prior to the application of pressure, but they must also be kept clean between the cleaning step and the pressure step. The present invention provides the only practical method of maintaining cleanliness; namely, the method of pressing the sealing surfaces together in the same chamber in which they were cleaned.

Perhaps in theory, perfectly smooth, perfectly clean sealing surfaces would bond together in a vacuum tight seal without the application of any pressure. However, the purpose of the invention being to provide a practical mass production-method of making electron tubes does not admit of such perfection. Thus, it is proposed that substantial pressure be used. One purpose of the pressure is to overcome the lack of smoothness. Clearly, if sealing surfaces which are not perfectly smooth are brought together, they will not be in contact over their entire surfaces but only at a number of separate points. Although the points in contact may bond together to form a joint of appreciable strength, they will very likely not form a continuous wall, or vacuum tight seal. The invention requires, then, that enough pressure be applied to assure sufiicient contact between the sealing surfaces to form a vacuum-tight seal. In addition, it has been found that the yield of good seals is increased if suflicient pressure is applied to actually cause radial deformation or extrusion of the sealing surfaces, or at least of the softer sealing surface where the surfaces are of different material. This improvement is believed to be explainable by the theory that any surface oxides which might not have been removed by the high temperature cleaning can be broken up by deformation to expose clean metal. This theory also provides an additional reason for using sealing surfaces having a finish which is rougher than an optical finish, the thought being that surface oxides can be more easily ruptured when relatively rough surfaces are pressed together than when optically smooth surfaces are used.

In connection with the application of pressure, it should be noted that the apparatus provides a very rapidly operating and simple arrangement. More specifically, the apparatus eliminates the need for complicated bellows arrangements by making the pressure exerting means or ram 82 movable with the chamber wall 80. Thus, the movement which initially closes the chamber places ram 82 almost in pressure exerting contact, and the movement which removes the pressure of ram 82 also opens the chamber so a finished tube can be immediately extracted. It is also important to note that when pressure is applied to the tube it is done with poor heat conductors such as ceramic pieces 98, 100, 102, and 82. There are two reasons for preventing a good heat conducting path; one is that it would be undesirable to drain heat from the sealing surfaces at the exact period of sealing, and the other reason is that sudden cooling of the tube ceramics would cause them to crack.

Utilizing the basic teachings of the invention, it is possible by experimentation to determine the minimum temperatures, pressures and duration of application which are necessary to obtain satisfactory seals between the various materials which might be used. By way ofexample, experiments have been made with tubes which comprise the following envelope construction: a high alumina ceramic member such as rings 11, a conventional molybdenum-manganese metallizing coating on the ceramic, and a nickel layer forming a sealing surface plated on the metallizing coating; a thin sealing ring of copper; and a metal envelope ring such as rings 1342 of Kovar or nickel. The metallizing, the nickel plating, and the copper rings do not appear in the drawing because the invention is not limited to any specific materials and because they are extremely thin. For example, the copper ring is .003 inch thick and the metallizing and nickel plating are each only .0002 inch thick. Tubes having satisfactory seals with these materials have been made according to the following procedure utilizing the apparatus of the invention: Place the tube parts in the vacuum chamber, exhaust the chamber, induce R.F. current in the sealing surfaces for about three minutes to raise the temperature of the surfaces to about 750 0., lower ram 82 with sufficient force to deliver between 11,000 and 18,000 pounds per square inch pressure at the sealing surfaces, and maintain this pressure for about two and one-half minutes. The cathode must be formed prior to applying pressure and the earlier it is formed the longer will be the period for emptying the tube of the gases given oif during forming.

Not only are the method and apparatus of the invention not limited to certain specific materials, they make it possible to effect pressure seals even using easily oxidized metals such as copper. The advantage of being able to use copper, which is a desirable metal in electron tubes, is made possible because the sealing surfaces are not re moved from the non-oxidizing environment between the time they are cleaned by heating and the time they are pressed together.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

l. A method of making electron tubes of the type having an envelope in which metal sealing surfaces are joined together to form a vacuum-tight seal, said method comprising the steps of placing the tube parts in a vacuumtight chamber, evacuating said chamber, heating said sealing surfaces while said chamber remains evacuated, and forcing said sealing surfaces together with a pressure substantially above the pressure obtainable by evacuating the interior of the tube and exposing the exterior to the atmosphere, the temperature to which said sealing surfaces are heated being less than the melting temperature of the surfaces.

2. A method of making electron tubes of the type having an envelope in which metal sealing surfaces are joined together to form a vacuum-tight seal, said method comprising the steps of forming said sealing surfaces with a finish rougher than an optical finish, placing the tube parts in a vacuum-tight chamber, evacuating said chamber, heating said sealing surfaces to clean them while said chamber remains evacuated, and forcing said sealing surfaces together with sufficient pressure to join them in a permanent vacuum-tight seal, the temperature to which said sealing surfaces are heated being less than the melting temperature of the surfaces.

3. A method of making electron tubes of the type having an envelope in which metal sealing surfaces are joined together to form a vacuum-tight seal, said method comprising the steps of placing the tube parts in a vacuumtight chamber, evacuating said chamber, heating said sealing surfaces by inducing a radio frequency current therein, and forcing said sealing surfaces together while .maintainingsaid sealing surfaces heated and while main- 'taining said "chamber evacuated, the temperature to V which. said sealing surfaces are heated being less thanthe meltingtemperature of the surfaces.

4. A method'of making electron tubes of the type hav- ,ing an envelope in which'metal sealing surfaces are joined together to form. a vacuum-tight seal, said method com- "prising the steps of placing the tube parts in a vacuumltight chamber, 'evacuating said chamber, heating said .sealing surfaces, and forcing said sealing surfaces to- "gether with suflicient pressure to deform at least one of fsaid sealing surfaces, thetemperature to which said sealing surfaces ,are heatedbeing less than the melting temj perature of the surfaces. I

, 5. A;'1ltleih0d of making electrontubes of the type havv ing an envelope inwhich relatively hard and soft metallic sealing surfaces are joined together to form a vacuumtight seal, said method comprising the steps of placing the tube parts in a vacuum-tight chamber, evacuating said chamber, heating said sealing surfaces by inducing a high frequencycurrenttherin, thenforcing said scaling surfaces together with-sufficient pressure to deform said relatively soft metal surface, the temperature to which said sealing surfaces areheated being less than the melting temperature of the surfaces.

6. A method of making electron tubes of the type f having anenvelope in which metal sealing surfaces are i joined together to form a vacuum-tight seal, said method faces, the temperature to which said sealing surfaces. are

heated being less than the melting temperature of the surfaces. 7 i

7. A method of making electron tubes of the type having an envelope in which metal sealing surfaces are joined together to form a vacuum-tight seal, said method comprisingthe steps of forming said sealing surfaces with a finish tougher than an optical finish," placing the tube parts in a vacuum-tight chambenobtaining a nonoxidizing atmosphere in said chamberfheatingsaidsealing surfaces while maintaining 'saidjnoh-oxidizing atmosphe're, and forcing said envelope parts together. with suflicient pressure to form a permanent vacuum-tight 'seal, the temperature to which said sealing surfaces are tight chamber, .maintaining a nonoxidizing atmosphere in .said chamber, heating said sealing surfaces while maintaining said nonoxidizing" atmosphere, and forcing said sealing surfaces, together with a pressure onsaid surfacesof at least 11,000 pounds per squareinchwhile said sealing surfaces are heated, the temperature to "which said sealing surfaces are heated being less than the melting temperature of the surfaces.

9. A method of making electron tubes of the type having an envelope in whichmetal sealing surfaces are joined together to form a vacuum-tight seal, said method comprising the steps of placing the tube parts in a. gastightjchamber, maintaining a nonoxidizing atmosphere in said chamber, heating said sealing surfaces While maintaining said nonoxidizing atmosphere, and forcinglsaid sealing surfaces togetherwith a pressure substantially above the pressure obtainable by evacuating the interior of the tube and exposing the exterior to the atmosphere,

the'temperature to which said sealing surfaces are heated being less than the melting temperature of the surfaces, one of said sealing surfaces being copper, and the adjacent sealing surface in contact with the copper being a metal which is harder than copper.

'10. A method of making electron tubes of the type having an envelope in which metal sealing'surfaces are 25 joined together to form a vacuum-tight seal, said method comprising the steps of placing the tube parts in a gastight chamber, maintaining a nonoxidizing atmosphere in said chamber, heating said sealing surfaces to about 750 C. while maintaining said'nonoxidizing atmosphere, and forcingsaid sealing surfaces together withya pressure onlthe sealing surfaces of at least 11,000 poundsv per square ,inch,-'the temperature to which said sealing surfaces are heated being less than the melting temperature off'the surfaces, and at least one of said sealing surfaces being copper. V

References Cited in the file of this patent I UNITED STATES PATENTS 2,259,165

Karasick Oct.14, 1941 2,412,836, Rose Dec. 17, .1946 2,450,130 Gordon Sept. 28, 1948 2,575,448 Haas Nov. 20,1951 2,731,578 McCullough Ian. 17, 1956 2,749,668 Chaft'otte et a1. June 12, 1956 2,752,532 Dussaussoy et a1. June 26, 1956 2,787,510' Breadner 'et a1. Apr. 2, 1957 2,792,271 'Beggs May 14,- 1957 2,837,396 Warren IuneB, 1958 2,855,265 Foot e Oct. 7, 1958 2,876,596 Kessler Mar. 10, 1959 1 I FOREIGN PATENTS 724,290 Great-Britain Feb. 16,1955

'UNETEE STATES PATENT @FFZCE @R'HFEQAT N Patent Nd. 2 996 34? August 15 1961 Jack A McCullough eta a1.

It is hereby certified that errer appears in ihe above numbered patenbrequiring correction and that the said Letters Patent should read as "corrected belcwn Column 1 line 50 for "for" read the (SEAL) Attest':

EEAVID L. LADD Commissioner of Patents ERNEST w. s DE Attesting Officer 

